1. Field of the Invention
The present invention relates to a control device for an internal combustion engine and, in particular, relates to a control device for an internal combustion engine which causes a fuel injection valve disposed at an air intake port to inject and supply atomized fuel during an air intake stroke.
2. Conventional Art
These days, requirements of environmental protection relating to automobiles including exhaust gas regulation and fuel economy regulation become strict day by day. Therefore, in order to enhance exhaust gas property and fuel economy a variety of internal combustion engines such as a lean burn engine and direct injection engine have been proposed.
The above direct injection engine requires a lot of alternation with respect to a base engine such as requirement of new surrounding devices other than the requirement of a piston head having a specific configuration and causes a problem of increasing a manufacturing cost. For this reason, a development activity improving combustion in an internal combustion engine by making use of a lean burn engine is, in particular, continued.
The lean burn engine is an engine which is designed to burn leaned air fuel mixture, in which fuel is injected in such engine through a plurality of fuel injection valves each provided for respective cylinders in synchronism with the air intake stroke, in that through a multi point injection (MPI) system, thereby, the leaning of the air fuel mixture is realized as well as a flammable rich air fuel mixture is concentrated only around an ignition plug and thus an enhancement of the exhaust gas property and the fuel economy is achieved.
Further, in order to enhance the exhaust gas property and the fuel economy for such internal combustion :engine, it is necessary to enhance the quality and formation of the air fuel mixture in the respective cylinders. For this purpose, a variety of technical measures of improving combustion in internal combustion engines are proposed, for example, such as in JP-A-11-13585 (1999) and JP-A-11-159424 (1999) by atomizing a droplet diameter of the fuel injected by a fuel injection valve below 70 xcexcm, by atomizing a droplet diameter of the injected fuel through the provision of multi aperture injection ports in the fuel injection valve and by injecting fuel at the center portion of the air intake port through the provision of a forwardly positioned injection port (through nozzle elongation).
Now, the above referred to conventional art intends to enhance the exhaust gas property and the fuel economy in the internal combustion engine by atomizing the droplet diameter of the injected fuel and further, by forwardly positioning the injection port in view of the facts that the deposition of the injected fuel such as at the intake port and at the cylinders deteriorates the exhaust gas property, in other words so as to resolve the wetness property of the fuel.
Although, through the atomization of the droplet diameter of the injected fuel the deterioration of the exhaust gas property due to deposition of the injected fuel such as on the cylinders is resolved, however, since the kinetic energy of the atomized injected fuel is small in comparison with that of the injected fuel having a usual droplet diameter, thus the so called penetration force of the injected fuel after being injected from the fuel injection valve until arriving into the concerned cylinder is also small so that there remains a problem of delaying time until arrival of the injected fuel into the cylinder.
The present inventors found out a problem that the above referred to time delay makes it difficult to inject the fuel immediately after or in other words in synchronism with the air intake stroke under the fuel injection system of MPI, in that the fuel has to be injected earlier, and necessity of taking a proper countermeasure for resolving the problem. The above referred to conventional art only takes into consideration of resolving the wetness of the fuel, but not takes into any particular consideration of resolving the time delay.
The present invention is completed in view of the above problems and an object of the present invention is to provide a control device for an internal combustion engine under a fuel injection system of MPI which enhances quality and formation of air fuel mixture in cylinders and resolves the time delay caused by the atomization of droplet diameter of the injected fuel.
A control device for an internal combustion engine according to the present invention which achieves the above object basically comprises fuel injection vales which are disposed at an air intake port for the internal combustion engine and inject fuel from the air intake port toward respective cylinders for the internal combustion engine; and an air flow velocity accelerating means which accelerates air flow velocity in the air intake port, wherein the fuel injection time from the fuel injection valves is controlled in synchronism with or immediately after an air intake stroke for the internal combustion engine as well as respective injection ports of the fuel injection valves are positioned at an accelerated air flow portion or near the accelerated air flow portion formed by the air flow velocity accelerating means, thereby, a time delay caused by atomization of the injected fuel is resolved.
According to the thus constituted control device for an internal combustion engine, since the fuel injected under the fuel injection system of MPI makes use of the accelerated air flow formed by the air flow velocity acceleration means as well as the fuel injection time is correctly set to synchronism with the air intake stroke, for example, even when there are restrictions with regard to the design and/or the attachment position of the fuel injection valves, the time delay due to the atomization of the injected fuel can be resolved as well as the quality and spatial formation of the air fuel mixture in the respective cylinders are enhanced, thereby, the exhaust gas property and fuel economy are enhanced.
Further, an embodiment of the control device for an internal combustion engine according to the present invention is characterized, in that the fuel injection time of the fuel injection valves is determined by setting a fuel injection start timing or a fuel injection completion timing during the air intake stroke, more specifically the fuel injection time is controlled by the fuel injection start timing or the fuel injection completion timing so that an optimum air fuel mixture is formed, the fuel injection time is set near the maximum air flow velocity occurring period when the air flow velocity in the air intake port is high or the fuel injection time is set before the maximum air flow velocity occurring period when the air flow velocity in the intake port is low.
In the thus constituted control device for an internal combustion engine according to the present invention, since the setting of the fuel injection time is altered depending on the air flow velocity in the air intake port, a fuel injection in an optimum air fuel mixture forming range can be realized, even if variation of combustion is caused depending on engine rpm and load, thereby, a fuel transportation delay due to droplet diameter atomization of the injected fuel is eliminated as well as the quality and spatial formation of air fuel mixture in the cylinders are further enhanced.
Further, another embodiment of the control device for an internal combustion embodiment is characterized, in that the device is provided with means for performing arithmetic operation of a revolution fluctuation index representing a combustion stability for the internal combustion engine and the setting of the fuel injection time of the fuel injection valves is corrected based on the arithmetic operation result by the means for performing arithmetic operation of the revolution fluctuation index.
In the thus constituted control device for an internal combustion engine according to the present invention, since the fuel injection valves are driven with reference to a signal from the means for performing arithmetic operation of a revolution fluctuation index, even if the fuel injection time deviates from one that forms an optimum air fuel mixture, the deviation can be corrected to ensure reliability of the internal combustion engine.
Still further, still another embodiment of the control device for an internal combustion engine is characterized, in that each of the fuel injection valves is provided with an elongated value main body so that all of the fuel injected from the respective injection ports is supplied into the respective cylinders, a distance from the respective injection ports to the respective cylinders are set depending on the atomized droplet diameter of the fuel to be injected from the respective injection ports, the respective valve bodies in the respective fuel injection valves are driven in a high speed so as to enhance atomization of the fuel injected from the respective injection ports as well as to uniformalize the droplet diameter of the fuel injected from the injection ports from the beginning of injection to the end thereof, and further characterized, in that the droplet diameter of injected fuel is controlled below about 70 xcexcm.
The thus constituted control device for an internal combustion engine according to the present invention can be adapted to a variety of internal combustion engines even when the available droplet diameter is different depending on the performance of the internal combustion engines in association with the above explained fuel injection valves having the elongated valve main body, thereby, the transportation delay of the injected fuel due to atomization is further eliminated. Further, in association with the above explained fuel injection time, in the present control device, the atomized fuel is injected in a short time at an optimum timing, the time delay of the injected fuel arrival due to atomization of the injected fuel droplet diameter is eliminated, as well as the quality and spatial formation of the air fuel mixture in the respective cylinders are further enhanced. Still further, with the above explained structure of the fuel injection valves the manufacturing cost of the device can be reduced by limited modification of such as base engine.